1. Field of the Invention
The present invention relates to a thermal line printer in which characters are printed on a recording paper, using a thermal line head having an array of heat generating elements.
2. Description of the Related Art
In a known thermal line printer, an entire line is printed on a recording paper such as a heat sensitive paper, in a single operation by means of a thermal line head which is comprised of a line of heat generating elements (e.g., resistors). The structure of a known thermal line printer is shown in FIG. 7 by way of example.
In FIG. 7, a conventional printer 100 includes a thermal line head 101 which has a plurality of heat generating resistors arranged along a line parallel to the printing paper and substantially perpendicular to the feeding direction of the printing paper, and a platen roller 102 opposed to the thermal line head 101. The thermal line head 101 and the platen roller 102 are housed in a body casing 100a which extends in a direction substantially perpendicular to the surface of the recording paper.
The recording paper, which is inserted in the printer 100 through an insertion opening 103 formed at the upper portion of the printer body, pressed at a predetermined pressure by and between the thermal line head 101 and the platen roller 102 and thereafter advanced in accordance with the rotation of the platen roller 102.
To press the printing paper at a desired pressure for the printing operation, the thermal line head 101 is swingable or rotatable about a shaft 101b (indicated by a dotted line) and is continuously biased by a spring 107 toward the platen roller 102.
Attempts have recently been made to make the thermal line printer thinner to thereby enable a user to carry the same in a bag or a briefcase, etc. As can be seen in FIG. 7, since the platen roller 102 is opposed to the thermal line head 101 in the direction corresponding to the thickness of the printer body, it is necessary to reduce the diameter of the platen roller in order to make the thermal line printer thinner.
The platen roller 102 includes a rigid core and a resilient cover made of a rubber material or the like, which surrounds the core to obtain a frictional force necessary to convey the printing paper together with the thermal line head 101. Therefore, if the diameter of the platen roller 102 is reduced, the diameter of the core is also reduced. However, the decrease in the diameter of the core of the platen roller causes the platen roller to tend to deflect when it is pressed. Thus, the diameter of the platen roller 102 has a minimal size, making it difficult to make the thermal line printer thinner.